Cathode rays are streams of electrons observed in vacuum tubes
At one end of a vacuum tube is a cathode, a thin wire filament through which is passed a high current, heating it so that electrons are released by thermionic emission and accelerated from the cathode towards an anode in the middle of the tube, resulting in a beam of electrons
The electrons travel in a straight line and hit the other end of the tube, causing the atoms they hit to glow with fluorescence
Since a cathode ray is a stream of electrons, it is deflected in the presence of an electric field
Simple treatment of cathode-ray oscilloscopes
A cathode-ray oscilloscope uses a cathode ray to generate a beam of electrons that is observed on a screen
It has a deflection system of two plates that deflects the electrons when there is a potential difference between them
There are two deflections systems for each direction called the X-plates and the Y-plates
A deflection system can be wired to a circuit to show the potential difference between two points in the circuit
The X-plates is commonly wired to a time-base circuit in the oscilloscope to show how the potential difference in the circuit changes with time